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Post‐ and presynaptic effects of norepinephrine in guinea‐pig colonic submucous plexus
Author(s) -
G. Dobreva,
Michel Neunlist,
Thomas Frieling,
Michael Schemann
Publication year - 1998
Publication title -
neurogastroenterology and motility
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.489
H-Index - 105
eISSN - 1365-2982
pISSN - 1350-1925
DOI - 10.1046/j.1365-2982.1998.00081.x
Subject(s) - phentolamine , yohimbine , norepinephrine , prazosin , medicine , endocrinology , postsynaptic potential , hyperpolarization (physics) , inhibitory postsynaptic potential , submucous plexus , chemistry , excitatory postsynaptic potential , stimulation , biology , dopamine , antagonist , receptor , myenteric plexus , immunohistochemistry , organic chemistry , nuclear magnetic resonance spectroscopy
Intracellular recording techniques were used to investigate the effects of norepinephrine on submucous neurones in the guinea‐pig distal colon. In 81% of the neurones, pressure microejection of norepinephrine produced a membrane hyperpolarization associated with a decrease in excitability and input resistance. Microejection of clonidine (1 μ m ) mimicked the norepinephrine‐induced hyperpolarization, whereas both phentolamine (1 μ m ) and yohimbine (1 μ m ) reversibly suppressed it. Superfusion of norepinephrine (1 n m – 10 μ m ) hyperpolarized the cells in a concentration‐dependent manner. Norepinephrine and clonidine (1 n m – 10 μ m ) caused a concentration‐dependent presynaptic inhibition of stimulus‐evoked cholinergic fast excitatory postsynaptic potential. Slow inhibitory postsynaptic potentials (sISPSs) were induced by focal electrical stimulation of the interganglionic fibre tracts in 43% of the neurones tested. Superfusion of both phentolamine (1 μ m ) and yohimbine (1 μ m ) reduced the sIPSPs while prazosin (1 μ m ) had no significant effect. We concluded that norepinephrine acted post‐ and presynaptically via α 2 ‐adrenoreceptors to have an inhibitory effect on the guinea‐pig colonic submucous. In addition, our study strongly supported the role of norepinephrine as a mediator of the sIPSPs. As a result, norepinephrine would primarily suppress information transfer within the neuronal circuits in guinea‐pig colonic submucosal plexus.